For a larger electronic device, such as a personal computer and a television, a car navigation device, a cell phone, a smaller electronic device such as an electronic dictionary, and a display device of an OA/FA device, use of a liquid crystal display element or a touch screen has become popular. In such a liquid crystal display element and a touch screen, as well as a device such as a solar cell, a transparent conductive film is used for a part of an interconnection, a pixel electrode or a terminal, which requires transparency.
As a material for a transparent conductive film, ITO (Indium-Tin-Oxide), indium oxide and tin oxide, which exhibit high transmittance for visible light, have been heretofore used. For an electrode of a substrate for a liquid crystal display element, a patterned transparent conductive film consisting of the above material has become mainstream.
As a patterning method of a transparent conductive film is common a method by which after the formation of a transparent conductive film, a resist pattern is formed by a photolithography, and a predetermined part of the conductive film is removed by wet etching to form a conductive pattern. In the case of an ITO and indium oxide film, a mixture solution consisting of 2 liquids of hydrochloric acid and ferric chloride is commonly used as an etching solution.
An ITO film or a tin oxide film is formed generally by a sputtering method. By this method, however, the properties of the transparent conductive film change sensitively depending on the difference of the sputtering method, a power or gas pressure of a sputter, a substrate temperature, or a type of the atmospheric gas. The difference of the film quality of a transparent conductive film caused by a fluctuation of the sputtering conditions can cause fluctuation in the etching speed, when the transparent conductive film is subjected to wet etching, which may lead to a lower product yield by reason of poor patterning. Further, the above method for forming a conductive pattern must go through a step of sputtering, a step of forming resist, and a step of etching, and therefore the process is long, which constitutes a heavy burden costwise.
To solve the above problem, an attempt has been made recently to use an alternative material to ITO, indium oxide, tin oxide, etc. to form a transparent conductive pattern. For example, in the following Patent Literature 1 is disclosed a method for forming a conductive pattern, by which a conductive layer containing conductive fiber such as silver fiber is formed on a substrate, then a photosensitive resin layer is formed on the conductive layer, the former is exposed to light from above through a pattern mask, and developed.